Achilles issue

Newbie here, training for my second 50-miler (the San Diego 50, Jan. 13).

Survived all the long runs pretty well, no real injuries...and then yesterday developed some pain in my left achilles, and a small bump at the site. Did 8 miles on it today, and could definitely feel it.

I know better than to seek actual medical advice on an internet forum (no offense... :) -- but any insight on achilles issues? (It's a first for me, in 26 years of marathon+ running.) All I have left is two weeks of tapering, then the race. My intention is to ignore it and keep going... but damned sure don't want an achilles tear.